This invention relates to the preparation of phenol, and more particularly to a phenol preparing process which can recover propylene from the acetone by-product and recycle the recovered propylene as the starting material.
It is well known in the art to react benzene with propylene to produce cumene, to oxidize cumene to produce cumene hydroperoxide, and to acid cleavage cumene hydroperoxide into phenol and acetone. A conventional phenol preparing process having these steps combined is generally known as the cumene process.
It is also an old well-known technique to hydrogenate acetone into isopropanol. This technique is still widely used at present for the assay of the catalytic activity of a hydrogenating catalyst and other purposes. For example, the activity of Raney nickel catalysts is often examined by comparing their acetone hydrogenating ability. Several advanced processes have been proposed as disclosed in Japanese Patent Application Kokai Nos. 12729/1987 and 77338/1987.
Nevertheless, insofar as the inventors know, it has never been proposed to produce isopropanol from the acetone by-product resulting from preparation of phenol by the cumene process, and to dehydrate the isopropanol into propylene.
There are known some analogous processes, for example, to produce ethylene from ethanol and to produce isobutylene from tert.-butanol. However, these olefin producing processes cannot be applied to the production of propylene from isopropanol for the following reason. Since propylene is substantially different in reactivity from ethylene or isobutylene, those skilled in the art cannot presume the dehydration of isopropanol from either the conditions for synthesis of ethylene from ethanol or the conditions for synthesis of isobutylene from tert.-butanol.
As to the reuse of the acetone which is by-produced in the cumene process, for example, by its conversion into propylene, no useful proposals have been made.
The phenol preparing process generally known as the cumene process is characterized by the production of acetone by-product, which is advantageous from some aspects, but disadvantageous from other aspects. More particularly, it is an advantage in that simultaneous production of two products in a single preparation unit is more efficient than individual production in separate units. In turn, if the proportion of phenol and acetone produced is unbalanced relative to their commercial demands, one for less demand is produced largely in vain.
As is known in the art, acetone is available in surplus for these years. Thus the production of acetone by-product is now considered as a serious drawback of the cumene process. Although acetone has found the majority of its application as a starting material for preparing methyl methacrylate, the demand for acetone is decreasing because of a switch of the starting material for preparing methyl methacrylate to another.
Under the circumstances, there is a need for the development of a phenol preparing process which is devoid of production of acetone and other by-products. Although several proposals have been made, there is available no process capable of preparing phenol in satisfactory yields.
In addition, impurities in propylene often cause a drawback during the preparing step of cumene from benzene and propylene in the cumene process for the preparation of phenol. That is, propylene for use in the cumene preparation is manufactured generally using crude oil as the starting material. Crude oil, however, contains sulfur compounds and various heavy metals, and these impurities are sometimes carried in propylene as trace contaminants during its manufacturing process. For example, carbonyl sulfide (COS) as a sulfur compound or As as a heavy metal contaminant in propylene inhibits function of a catalyst (aluminum chloride-HCl complex) for use in the cumene preparation, thus disturbing normal progress of the cumene synthesis. Therefore, a strict purification process is perproduced to avoid contamination of propylene with these impurities. Types and quantity of these contaminants, however, vary depending on not only the crude oil source but also the difference in the process conditions for the preparation of propylene from crude oil. Such irregularity burdens the propylene purification process with exceptionally complex and severe steps.
In consequence, a process for the preparation of propylene with highly stable purity containing no such impurities has been expected to be established, for the purpose of reducing the extreme burden of steps in the propylene purification process.